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'[PIC]: Propellor Clock'
2002\08\29@195416 by Tony Nixon

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Hi all,

Well I got my wings presented to me the other night :-)


They were supposed to raffle the propellor clock I donated for the
runway sealing fund raiser, but due to other raffles, it was decided
that it was a bit too much to expect from everyone, so it will be
raffled another time.

It sure made a few eyes pop out and I'm sure the raffle will go off
well. I've already been asked to make more and the president of the
club, who is also a QANTAS captain, wants two. I knew this would happen,
and I'm not sure I can put a price on something that took that long to
make.

Anyway, the tinkerer that I am, I have designed a simpler way (yet to be
tested) and I told them I "would see".

As part of my circuit, I used a relay to convert a full wave rectified
AC input to a half wave to detect when the "time set" switch is pressed.
This is just a series diode being switched in and out of a leg of the AC
path to the full wave rectifier.

Is there a way to do this without a relay?


One interesting spin off, was that I got asked to help out with the
instrument flight rules simulator that they are building.


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Tony

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2002\08\29@201218 by Olin Lathrop

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> As part of my circuit, I used a relay to convert a full wave rectified
> AC input to a half wave to detect when the "time set" switch is pressed.
> This is just a series diode being switched in and out of a leg of the AC
> path to the full wave rectifier.

I assume the real question is how to get user input to the spinning part?
If so, there are a number of ways.  We use an IR led/detector in a similar
product.  How are you getting power to the rotating board?


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2002\08\29@204658 by Dave Dilatush

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Tony wrote...

>As part of my circuit, I used a relay to convert a full wave rectified
>AC input to a half wave to detect when the "time set" switch is pressed.
>This is just a series diode being switched in and out of a leg of the AC
>path to the full wave rectifier.

Relay... Ugh.  Click, click.  Bad.  <SHUDDER>

>Is there a way to do this without a relay?

Yes.

The series diode that you're switching in and out with that
mechanical... "thing" could be replaced by a power mosfet.  When
its gate is biased so as to turn the mosfet ON, it conducts
current on both halves of the cycle; when the gate is biased to
turn it mosfet OFF, it conducts only in one direction, through
the intrinsic substrate diode.

Whether you use a p-channel or n-channel device, which direction
you face it, and how to arrange the gate drive are all things
that depend on the circuit details.

DD

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2002\08\29@205507 by Tony Nixon

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Olin Lathrop wrote:
>
> > As part of my circuit, I used a relay to convert a full wave rectified
> > AC input to a half wave to detect when the "time set" switch is pressed.
> > This is just a series diode being switched in and out of a leg of the AC
> > path to the full wave rectifier.
>
> I assume the real question is how to get user input to the spinning part?
> If so, there are a number of ways.  We use an IR led/detector in a similar
> product.  How are you getting power to the rotating board?

12VAC power if fed by 2 slip rings.

The 50Hz AC wave form also suppies timing for the clock.

100 pulses/sec = no press
50 pulses/sec = press

I have an IR LED already to detect radial position.

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2002\08\29@210321 by David Duffy

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Tony wrote:
<snip>
>As part of my circuit, I used a relay to convert a full wave rectified
>AC input to a half wave to detect when the "time set" switch is pressed.
>This is just a series diode being switched in and out of a leg of the AC
>path to the full wave rectifier.
>
>Is there a way to do this without a relay?

How about an SCR (in anti-parallel with the existing diode) with an opto
for control isolation if required.
Regards...

___________________________________________
David Duffy        Audio Visual Devices P/L
U8, 9-11 Trade St, Cleveland 4163 Australia
Ph: +61 7 38210362   Fax: +61 7 38210281
New Web: http://www.audiovisualdevices.com.au
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2002\08\29@232029 by Dale Botkin

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On Fri, 30 Aug 2002, Dave Dilatush wrote:

> The series diode that you're switching in and out with that
> mechanical... "thing" could be replaced by a power mosfet.

Yeah...  Dave like MOSFETs.  8-)  'Course he's right too.  My yard lights
tell me so every night.

Dale

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2002\08\30@024427 by Dmitriy A. Kiryashov

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Hi Olin and guys.

I have a feeling that there is way to transfer AC power
to rotating board without any contacts. Am I right ? ;)

The only problem I can see is start up... thought.. if power
consumption is linear function to speed of rotation it looks
easy to stabilize on both sides. Or feedback thru some code,
probably manchester, which is easy to send thru "decoupling"
transformer.

Nice project to improve mechanical skills ;)


WBR Dmitry.

PS.

Also how to get rid of opto sensor of "null" position ?




Olin Lathrop wrote:
>
> How are you getting power to the rotating board?

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2002\08\30@052534 by Alan B. Pearce

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>As part of my circuit, I used a relay to convert a full wave rectified
>AC input to a half wave to detect when the "time set" switch is pressed.
>This is just a series diode being switched in and out of a leg of the AC
>path to the full wave rectifier.
>
>Is there a way to do this without a relay?

Use a pair of optoisolators with the diodes wired in inverse parallel. If
both are on, then no button is pressed. If only one is on then a button is
pressed.

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2002\08\30@060706 by Russell McMahon

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> I have a feeling that there is way to transfer AC power
> to rotating board without any contacts. Am I right ? ;)

The equivalent of a transformer with one fixed and one rotating winding is
easily achievable and these are in commercial use. In this case it would be
feasible to have an inductive  power tranfer facility at only one point on
the rotation as the power required is low.

You could even rotate the shaft with the whole electronic assembly attached
and use fixed magnets on the "stator" and a coil on the rotor and
effectively produce an alternator. With the opposite coil/magnet
arrangement, equipment that I make controllers for produces over 300 watts
with a 200mm odd ferrite-magnet-lined rotor. A few watts would be very easy.


       Russell McMahon

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2002\08\30@061553 by Michael Rigby-Jones

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{Quote hidden}

If you use four individual rectifiers instead of a full bridge, you could
use a MOSFET to switch one  of the the rectifiers on the negative side to
ground.

Regards

Mike

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2002\08\30@073313 by Olin Lathrop

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> 12VAC power if fed by 2 slip rings.

Hmm.  You may be in for some long term problems with this approach.  There
is a commercial product out there that uses slip rings.  They have problems
with both noise and reliability.

> The 50Hz AC wave form also suppies timing for the clock.
>
> 100 pulses/sec = no press
> 50 pulses/sec = press

As someone else already pointed out, you could use a FET in the right place
to achieve the same effect.  Another possibility is to pass DC to the rotary
board and then superimpose a digital data stream on it.  This can supply
both clock and control information.


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2002\08\30@075020 by Olin Lathrop

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> I have a feeling that there is way to transfer AC power
> to rotating board without any contacts. Am I right ? ;)

Yes, we use a contactless method.


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2002\08\30@090956 by Bob Ammerman

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Or you can couple a higher frequency signal onto the power and pick it back
off on the board.

Bob Ammerman
RAm Systems

{Original Message removed}

2002\08\30@103240 by M. Adam Davis

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Tony Nixon wrote:

>Hi all,
>
>Well I got my wings presented to me the other night :-)
>
>
Congradulations!

>As part of my circuit, I used a relay to convert a full wave rectified
>AC input to a half wave to detect when the "time set" switch is pressed.
>This is just a series diode being switched in and out of a leg of the AC
>path to the full wave rectifier.
>
>Is there a way to do this without a relay?
>
>
Yes.  It's called a Silicon Controlled Rectifier (SCR).  When the scr is
triggered it stays on until the current is zero, and dureing its on time
it acts as a diode.  This is very useful in AC applications as the
current falls to zero 120 times a second.

Put two SCRs in anti parallel in series with the AC line.  Turn them
both on to get full AC.  Turn one off to rectify the AC to DC going one
direction, turn the other off to rectify it the other way, turn both off
to turn the AC off completely.

A triac is essentially two SCRs in anti-parallel with their triggers
connected together.  You're building a triac with two triggers.

-Adam

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2002\08\30@133855 by Peter L. Peres

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On Fri, 30 Aug 2002, Dmitriy A. Kiryashov wrote:

>I have a feeling that there is way to transfer AC power
>to rotating board without any contacts. Am I right ? ;)

Yes, there are rotary transformers. Also what you were thinking of but
using ac not dc for the stator windings. This helps with startup. In
theory it would be possible to build a custom rotor for a shaded pole ac
motor that contains power pickoff coils in the rotor besides the squirrell
cage. Such motors are made for fans, they have the rotor fully accessible
for hacking (the bearings are all on one side).

>Also how to get rid of opto sensor of "null" position ?

By making a notch in the magnetics so the field drops or increases at a
certain angle.

Peter

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2002\08\30@142238 by Peter L. Peres

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On Fri, 30 Aug 2002, Olin Lathrop wrote:

>As someone else already pointed out, you could use a FET in the right place
>to achieve the same effect.  Another possibility is to pass DC to the rotary
>board and then superimpose a digital data stream on it.  This can supply
>both clock and control information.

There is also the way used in some model trains. The voltage is upped for
a few miliseconds to change a bistable relay. It could be used by lowering
the voltage, f.ex. by having two antiseries zeners shorted by a NC button
for ac.

Peter

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2002\08\30@142841 by Brendan Moran

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How's this scheme *dons flame retardant armour*  It takes 2 micros (looks
like everything with me does ;) Use a permanent magnet on the vertical mount
of the shaft of the clock, and put two coils in the propeller; one on each
blade.  Use those to generate power.

Now, there are two ways of connecting the communications between the prop
micro and the stationary micro.  One could be done via AM modulation of a
UART signal, and using the power coils as a receiver, the other way, which I
like better, would be to put an LED on the base, aimed at the propeller, and
a photo-transistor on the propeller fairly near the shaft, so that it
doesn't move much.  Let the micro on the bottom do the tracking of the prop
position by putting a little shiny bit on the back of the prop, and have the
static micro transmit a packet (or more, depending on possible transfer
speeds vs. rotation speed) via the LEDs once per rotation then use the
interrupt generated by the UART receive to trigger the display sequence.

Rough guesstimate on feasability: Assuming that the propeller rotates at
say... 10 revs/s (I think that's enough to give a visible refresh), that's
600 RPM, then, say the photo-transistor is in receive range for 1/4 of the
cycle, that gives it 1/10/4 = 0.025s to get a burst off.  At 115200bps, on
10-bit frame (start, 8-data, stop), a single byte transmission takes
10/115200 = 87us, which should give way more than enough time to send all
the data required for all the letters you can display on your clock, and
since the timing is so small, the position error should be minimal.

And the static micro can do all the timekeeping, etc, leaving the prop micro
to do fancier letters/numbers/graphics

Now, using that, you can connect the static micro to a PC, and display
whatever you want on the propeller, not just the time ;)

On a related note,
I had a thought on how to drive a light wand to oscillate at high enough
freqency to display something (anything?) and wanted to hear if anyone
thought it would work:  put a farily light weight magnet on the bottom of
the wand, then put a coil connected to the mains--the way a cheap aquarium
air pump is--which would make the wand go back and forth across the display
range 120x per second.  This should produce a fairly nice, solid disply, I
think.  Higher refresh rate than my monitor, too ;o)

--Brendan

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2002\08\30@151903 by Peter L. Peres

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>As part of my circuit, I used a relay to convert a full wave rectified
>AC input to a half wave to detect when the "time set" switch is pressed.
>This is just a series diode being switched in and out of a leg of the AC
>path to the full wave rectifier.

I can't picture where you use a relay. Use a switch to cut out a diode
(normally closed switch). The same function can be implemented using a PNP
in series with the diode, a FET, a thyristor, even a photodarlington if it
has to be (for lower power circuits).

Peter

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2002\08\30@170529 by Dave Dilatush

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Dale wrote...

>On Fri, 30 Aug 2002, Dave Dilatush wrote:
>
>> The series diode that you're switching in and out with that
>> mechanical... "thing" could be replaced by a power mosfet.
>
>Yeah...  Dave like MOSFETs.  8-)  'Course he's right too.  My yard lights
>tell me so every night.

Did you get those low on-resistance MOSFETs yet to cure the heat
problem?  IIRC, your original pair were getting hotter'n a
two-dollar pistol, and the replacements were expected to run
lukewarm.  Do they?

In the case of the propeller clock, I was wondering: why
complicate things by running AC through the slip rings?  Why not
rectify and filter the transformer first, then run the filtered
DC through the rings.  Easier to modulate than this
now-you-see-it-now-you-don't trick with the diode.

DD

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2002\08\30@171350 by Dale Botkin

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On Fri, 30 Aug 2002, Dave Dilatush wrote:

> Dale wrote...
>
> >Yeah...  Dave like MOSFETs.  8-)  'Course he's right too.  My yard lights
> >tell me so every night.
>
> Did you get those low on-resistance MOSFETs yet to cure the heat
> problem?  IIRC, your original pair were getting hotter'n a
> two-dollar pistol, and the replacements were expected to run
> lukewarm.  Do they?

More or less.  More than lukewarm, but not plastic-melting hot either.
IRLZ34's are kinda toasty but manageable with about 8-9A of current.  The
next rev board will have provisions for two pair and heat sinks (which I'm
using now, but little bitty ones).  It's been running a couple of months
now without any drama.

Dale

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2002\08\30@173311 by Peter L. Peres

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On Fri, 30 Aug 2002, Dave Dilatush wrote:

>In the case of the propeller clock, I was wondering: why
>complicate things by running AC through the slip rings?  Why not
>rectify and filter the transformer first, then run the filtered
>DC through the rings.  Easier to modulate than this
>now-you-see-it-now-you-don't trick with the diode.

He is using the ac as timebase.

Peter

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2002\08\30@175014 by Peter L. Peres

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On Fri, 30 Aug 2002, Dale Botkin wrote:

>On Fri, 30 Aug 2002, Dave Dilatush wrote:
>
>> Dale wrote...
>>
>> >Yeah...  Dave like MOSFETs.  8-)  'Course he's right too.  My yard lights
>> >tell me so every night.
>>
>> Did you get those low on-resistance MOSFETs yet to cure the heat
>> problem?  IIRC, your original pair were getting hotter'n a
>> two-dollar pistol, and the replacements were expected to run
>> lukewarm.  Do they?
>
>More or less.  More than lukewarm, but not plastic-melting hot either.
>IRLZ34's are kinda toasty but manageable with about 8-9A of current.  The
>next rev board will have provisions for two pair and heat sinks (which I'm
>using now, but little bitty ones).  It's been running a couple of months
>now without any drama.

As I said in a previous posting, you can down the heating and use tiny
devices (even SMD) by putting many (not two) in parallel. For one offs
like yours, this is very easy. Order 10 fets and connect them 5+5 in
parallel. You can use TO220 cases with vertical mount (not laying down) so
they align. The dissipation goes way down very fast. P=I^2*R as you know,
25 times in the case of 5+5. For example there are RC power controllers
that can handle 300A at 7.5V with microminimal losses. They have 15 or
more SMD fets mounted w/o heatsink ... board and wire self heating are
more of a problem at these currents.

Peter

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2002\08\30@190309 by Dave Dilatush

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Peter wrote...

>On Fri, 30 Aug 2002, Dave Dilatush wrote:
>
>>In the case of the propeller clock, I was wondering: why
>>complicate things by running AC through the slip rings?  Why not
>>rectify and filter the transformer first, then run the filtered
>>DC through the rings.  Easier to modulate than this
>>now-you-see-it-now-you-don't trick with the diode.
>
>He is using the ac as timebase.

Duh.  Guess I could have figured that out for myself... :)

DD

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2002\08\31@092558 by Olin Lathrop

face picon face
> >He is using the ac as timebase.
>
> Duh.  Guess I could have figured that out for myself... :)

I think your idea still makes sense, Dave.  You have to have the rectifiers
and cap someplace.  It might as well not be on the rotating board.  I don't
think it would be hard to superimpose a serial bit stream on the power
connection.  This could be fed straight into the UART after detection, using
the slowest possible baud rate.  Timing information can be transmitted as
data, and only needs to be communicated every second.


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2002\08\31@112430 by Peter L. Peres

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On Sat, 31 Aug 2002, Peter L. Peres wrote:

>As I said in a previous posting, you can down the heating and use tiny
>devices (even SMD) by putting many (not two) in parallel. For one offs
>like yours, this is very easy. Order 10 fets and connect them 5+5 in
>parallel. You can use TO220 cases with vertical mount (not laying down) so
>they align. The dissipation goes way down very fast. P=I^2*R as you know,
>25 times in the case of 5+5. For example there are RC power controllers

My turn to write bs. The dissipation decreases only 5 times not 25 as I
wrote, using 10 devices instead of 2.

Peter

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2002\08\31@144906 by Dave Dilatush

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part 1 1577 bytes content-type:text/plain; charset=us-ascii (decoded 7bit)

Olin wrote...

>> >He is using the ac as timebase.
>>
>> Duh.  Guess I could have figured that out for myself... :)
>
>I think your idea still makes sense, Dave.  You have to have the rectifiers
>and cap someplace.  It might as well not be on the rotating board.

Good point.

>I don't
>think it would be hard to superimpose a serial bit stream on the power
>connection.  This could be fed straight into the UART after detection, using
>the slowest possible baud rate.  Timing information can be transmitted as
>data, and only needs to be communicated every second.

Yeah, I was wondering whether superimposing data and DC power
would really be all that difficult.

Noodling on it a bit, I came up with the attached.

The diode string D2 through D4 sets the amplitude of the
transmitted data stream.  D5 and C2 "hold up" the DC supply on
the propeller side during data transmission.  D6 provides MARK
level restoration for the receiver, so long data streams don't
get garbled by the AC coupling of C3.  C4 provides some level of
noise filtering, and should be as large as possible short of
interfering with data reception.  R4 provides a bit of DC
hysteresis in the receiver to help further reject noise.

The values shown should provide good operation from 1200 baud to
about 4800 baud; if lower data rates are used, C3 and C4 should
be increased proportionally.

The filter cap values might need some tweaking, so supply ripple
and load transients don't interfere with the data.

DD



part 2 6500 bytes content-type:image/gif; name=propdata.gif (decode)


part 3 144 bytes
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2002\08\31@144915 by Dave Dilatush

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Peter L. Peres wrote...

>On Sat, 31 Aug 2002, Peter L. Peres wrote:
>
>>As I said in a previous posting, you can down the heating and use tiny
>>devices (even SMD) by putting many (not two) in parallel. For one offs
>>like yours, this is very easy. Order 10 fets and connect them 5+5 in
>>parallel. You can use TO220 cases with vertical mount (not laying down) so
>>they align. The dissipation goes way down very fast. P=I^2*R as you know,
>>25 times in the case of 5+5. For example there are RC power controllers
>
>My turn to write bs. The dissipation decreases only 5 times not 25 as I
>wrote, using 10 devices instead of 2.

Yes, but the power dissipation per device does indeed go down by
a factor of 25.  And that's what matters most, eh?

DD

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2002\08\31@145251 by Roman Black

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Peter L. Peres wrote:
> >Order 10 fets and connect them 5+5 in
> >parallel. You can use TO220 cases with vertical mount (not laying down) so
> >they align. The dissipation goes way down very fast. P=I^2*R as you know,
> >25 times in the case of 5+5. For example there are RC power controllers
>
> My turn to write bs. The dissipation decreases only 5 times not 25 as I
> wrote, using 10 devices instead of 2.


But dissipation *per device* does decrease by
25 times. So you were 1/5 right! ;o)
-Roman

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2002\08\31@145322 by Roman Black

flavicon
face
Russell McMahon wrote:

> You could even rotate the shaft with the whole electronic assembly attached
> and use fixed magnets on the "stator" and a coil on the rotor and
> effectively produce an alternator.


What about using a cheap "toy" type DC motor,
with the spinning clock PCB attached to the BODY
of the motor. The shaft is secured and stays
stationary, so when the thing is spun by another
motor and belt, the first motor acts as a DC
generator and powers the PCB. You can get these
motors in a round can, and use the belt from motor
2 directly on the round can of motor 1 to spin it.
-Roman

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2002\08\31@150159 by Olin Lathrop

face picon face
> My turn to write bs. The dissipation decreases only 5 times not 25 as I
> wrote, using 10 devices instead of 2.

Total dissipation goes down proportional to the number of FETs in parallel
(assuming roughly equal current sharing).  Therefore dissipation per device
goes down proportional to the number of FETs squared.  I assumed that's what
you were talking about since the temperature of the FET and heat sinking was
the point of discussion.  In that case you were right the first time.


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2002\08\31@153938 by Olin Lathrop

face picon face
> Noodling on it a bit, I came up with the attached.

Looks good.  Pretty simple and cheap too.


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'[PIC]: Propellor Clock'
2002\09\01@140933 by Peter L. Peres
picon face
On Sun, 1 Sep 2002, Roman Black wrote:

>Peter L. Peres wrote:
>> >Order 10 fets and connect them 5+5 in
>> >parallel. You can use TO220 cases with vertical mount (not laying down) so
>> >they align. The dissipation goes way down very fast. P=I^2*R as you know,
>> >25 times in the case of 5+5. For example there are RC power controllers
>>
>> My turn to write bs. The dissipation decreases only 5 times not 25 as I
>> wrote, using 10 devices instead of 2.
>
>
>But dissipation *per device* does decrease by
>25 times. So you were 1/5 right! ;o)

20% was not a passing score where I come from ;-(

Peter

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2002\09\01@194330 by Tony Nixon

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picon face
Hi all,

Thanks for the help with the clock.

I decided to switch the AC with a SCR. It seems the simplest.

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2002\09\02@095607 by Dave Dilatush

picon face
Tony wrote...

>I decided to switch the AC with a SCR. It seems the simplest.

It might be, but then again it might be a bit tricky.

If the load behind your full-wave bridge is resistive (i.e., this
isn't a rectifier-filter combination), then simply pulsing the
gate of the SCR shortly after each zero crossing of the incoming
AC will suffice to turn the SCR on and keep it on for the
duration of the half-cycle.

However, if (as I suspect) your full-wave bridge is feeding a
filter capacitor, it gets a little more complicated: an SCR,
after being triggered, only conducts so long as current is being
drawn through it- and current flow occurs in a rectifier/filter
circuit only near the peaks of the incoming AC and it is at these
peaks where you would have to trigger the SCR.  Otherwise, it
will never turn on.

The width of the current peaks depends on the transformer winding
resistance, how big the filter capacitors are, and how much DC
load current is being drawn, and they can be VERY brief.

DD

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2002\09\02@154427 by Peter L. Peres

picon face
Get a PFET or NFET and connect it in series to the existing low voltage ac
line. Its reverse diode will do the reverse conduction, and you will need
a resistor to power the gate and a NO switch to short G and S. Depending
on your current you could use any IRFxxxx fet. See what you have in store,
2A and up should be enough. The FET will run slightly warm (because one
semiperiod goes through the body diode). You can avoid this by using a
small rectifier scheme to drive G but you don't need to.

Peter

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2002\09\02@230337 by Tony Nixon

flavicon
picon face
Dave Dilatush wrote:
{Quote hidden}

What about an opto coupled SCR. Wouldn't that stay "active" only while
the LED was on?

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2002\09\03@052425 by Dave Dilatush

picon face
Tony wrote...

>What about an opto coupled SCR. Wouldn't that stay "active" only while
>the LED was on?

Dunno.  I've never used one of those.  If you can obtain one
that'll withstand the rms current you're trying to pass, that
might work.

DD

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